Step 1: Painting...
Step 2: Making it shoot...
2 index cards
1 pen that has a hollow inside (barrol)
1 roll of scotch tape
take the 2 index cards and roll them up into a cylinder, you wanna make the index cards have no space in bewteen the pen body. Put the pen's body down the barrol of the nerf gun (in the cross looking thingy). Then make sure you tape it up good. Also make sure that its down all the way in the barrol and air tight. You should be able to place the airsoft bb in down the barrol and shoot. If you have a gap in between, then you want to fill it up with more paper/index cards. This is what you should've made before placing it in the barrol.